As with all audio evaluations the way to do it properly isn't to hold a low quality cell phone mic up in the air and move it around during the recording..
It should be done in the electrical domain, level matched, and not perceptually compressed by Youtube's FLV process. [I suspect the cellphone uses perceptual codec compression too, plus on top of that dynamic range compression, AGC, so any level changes and "punch" we hear can not reliably be attributed CD vs. LP, even if we pretend to think the sound on the LP and CD came from the same master which it hardly ever does.
If one has a gun to their head and has no means to use anything other
than a cellphone, here's how you do it:
A. Set up the cellphone on a rigid tripod and don't move it at all between recording sessions. Aim the mic forward towards the sound source, not away from it towards you.
B. Close the room windows, turn off the building HVAC, hard drives, fans, and refrigerators, etc..
C. To avoid recording the room acoustics, at least as much as possible (a tremendous coloration), move the speakers together as much as possible and get that mic up close in the same typical triangular placement.
D. The recording distance should be the minimum possible such that the sound of the tweeter, (midrange), and woofer are still
well integrated [i.e., if you are too close you hear too much tweet or too much woof], usually this means a foot or two depending on the driver spacing.
E. If your cellphone can take external mics, do that.
F. If you have an option for manual record level instead of AGC, use that.
G. If the cell phone has either a wind cut filter or a noise reduction circuit, turn them off.
Also don't forget to use perfect speakers and a perfect cartridge, otherwise those things may alter the recording.